1. Field of the Invention
This invention relates to a method for the chemical vapor deposition of one or more metal oxides on a substrate, e.g. glass, and to the articles, e.g. neutral low emissivity coated glass, made thereby.
2. Description of the Relevant Art
It is known in the art that when a film of a transparent metal oxide, such as tin oxide, is deposited on a glass substrate, the coated glass substrate has non-uniform light reflection across the visible spectrum because of the difference in the refractive indices of the metal oxide and the glass substrate. In addition, when the thickness of the metal oxide coating is not uniform, the coating tends to display a multiplicity of interference color effects commonly referred to as iridescence. Such iridescence effects render the coated glass aesthetically unacceptable for most architectural applications. Thus, various methods to mask such iridescence effects and/or reduce reflectance have been proposed.
One technique for minimizing or eliminating the effects of the difference between the refractive indices of a metal oxide and a glass substrate is disclosed in U.S. Pat. No. 3,378,396 to Zaromb, wherein a glass substrate is coated by simultaneously directing separate sprays of a tin chloride solution and a silicon chloride solution onto a stationary heated glass piece in an oxidizing atmosphere, e.g. air. The heat of the glass piece thermally converts the metal chlorides to their metal oxides. The ratio of the two sprays is gradually varied to vary the ratio of the weight percent of the metal oxides in the coating. The resultant coating has a continuously-changing composition throughout its thickness, e.g. near the glass-coating interface, the coating is predominantly silicon oxide, the surface of the coating farthest from the glass-coating interface is predominantly tin oxide, and between the surfaces the coating is made up of varying weight percent amounts of silicon oxide and tin oxide. U.S. Pat. Nos. 4,206,252 and 4,440,882 further teach the depositing of fluorine-doped tin oxide on a gradient coating of the type taught by Zaromb.
U.S. Pat. Nos. 4,187,336 and 4,308,316 disclose the reduction of iridescence of a tin oxide coating on a glass substrate by the use of an intermediate coating between the tin oxide coating and the glass substrate having a thickness and refractive index satisfying the optical equation: the refractive index of the intermediate coating is equal to the square root of the refractive index of the glass substrate times the refractive index of the tin oxide coating.
U.S. Pat. Nos. 4,377,613 and 4,419,386 disclose a reduction in iridescence arising from a tin oxide film on a glass substrate by providing two intermediate coating layers between the glass substrate and the tin oxide. The intermediate layer next to the surface of the glass substrate has a high refractive index, while the intermediate layer farther from the surface of the glass substrate and next to the tin oxide film has a lower refractive index.
U.S. Pat. No. 4,853,257 discloses a method and an apparatus for depositing a low emissivity film on a glass ribbon by directing metal-containing coating reactants in vapor form onto the upper surface of a glass ribbon while the glass ribbon is supported on a molten metal bath contained in a non-oxidizing atmosphere. The carrier gas, the unreacted coating composition and any decomposition by-products are removed from the coating zone by an exhaust orifice on each side of, and equidistant from, the position where the coating reactants in vapor form are directed toward the glass ribbon.
U.S. Pat. No. 4,386,117 discloses a process for depositing a mixed metal oxide coating on a glass substrate by directing a gaseous mixture onto a moving glass ribbon and then exhausting gases from the coating zone at two locations equidistant from the entry of the gaseous mixture into the coating zone.